Along with a constantly growing rate and capacity of data traffic, layered network deployment has been introduced for a higher data rate, an extended network capacity and a lower traffic cost. With the layered network deployment, there is provided a low-power local evolved Node B (eNB) in addition to a macro eNB. The local eNB with a small coverage area is embodied in the femto/pico/relay form.
Since the coverage area of the local eNB is so small that a User Equipment (UE) is handed over at a much higher frequency and for a much larger number of times, a network deployment scheme with separation of the user plane from the control plane has been introduced for a lower frequency at which the UE is handed over between a macro cell hosted by the macro eNB and a small cell hosted by the local eNB. As illustrated in FIG. 1, there is underlying coverage by the macro cell and hotspot coverage by the small cell, and a data/signaling interface (a wired/wireless interface) is present between the small cell and the macro cell. When the UE connected with the macro eNB comes close to the cell controlled by the local eNB, the user plane can be handed over to the local eNB for a higher quality of service available from the local eNB; and when the UE goes far way from the cell controlled by the local eNB, the user plane needs to be handed over to the cell controlled by the macro eNB to maintain the wireless connection.
In the network architecture above with bearer separation, when the UE resides in the area covered only by the macro cell, both control plane connections of the UE and user plane connections, i.e., Data Radio Bearers (DRBs), are served by the macro eNB; and when the UE moves to the area covered by both the macro cell and the small cell, all or a part of the user plane connections of the UE are handed over to the local eNB for a higher traffic transmission rate while the control plane connections are still maintained with the macro eNB to thereby prevent a call of the UE from being dropped due to a failure to handed over the control plane connections.